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Hibernation in Turtles

As fall and winter arrive and the days grow shorter, your tortoise or box turtle will begin to slow down. Before long, he may go into hibernation, the dormant state when certain animals “sleep,” with a corresponding drop in body temperature and metabolism. This is his way to pass winter, when foraging is limited and it is more beneficial to save energy.

But why would a happy, healthy reptile with plenty of food and comfortable, even temperatures need to hibernate?

We are only beginning to understand the physiology of hibernation in reptiles, but it is becoming clear that it has health benefits. Healthy specimens deposit fat stores in preparation for hibernation. If not allowed to hibernate, these animals may be at risk for obesity. Hibernation is believed to be necessary for the normal function of the thyroid gland. There is also evidence that hibernation helps maintain the immune system. Hibernation is most likely required if a tortoise is to achieve his expected life span.

In their natural environments many box turtles and true tortoises hibernate from October or November until late February, March or even early April. The natural shortening of day length and the reduced brightness of daylight, as well as the decreased availability of food, are among the cues that induce hibernating behavior. The animals burrow deep in leaf litter or soft earth, which insulates them from temperature changes, and as the days lengthen and temperatures rise, they emerge in the spring.

For most tortoises, peak activity occurs between 70 and 85 degrees Fahrenheit (22 to 28 degrees Celsius). This is the animal’s POTZ (preferred optimal temperature zone). At temperatures below 68 F, activity levels decrease. When temperatures fall below 60 F, hibernation may occur.

To Hibernate or Not to Hibernate

Not all tortoises and turtles hibernate. In fact, hibernation patterns can vary from individual to individual. In captivity, with constant temperatures and plentiful food, they may not go into hibernation at all. In this, reptiles follow their own rules. Encouraging captive reptiles to hibernate often requires simulated conditions, such as gradually reducing temperature and light.

You should first make sure that the species you own is one that does hibernate. First, identify with certainty the species and, in some cases, the subspecies you own. Familiarize yourself with his natural history, origin and whether this individual would be likely to hibernate in the wild. Reptile veterinarians, experienced keepers, breeders, local reptile clubs and organizations such as The Tortoise Trust can be excellent sources of practical information. Unless you know that your pet is a member of a species that does not hibernate, you can be fairly certain that he should.
The most significant sign that your tortoise wants to hibernate is a decrease in his appetite. If his environment allows, he may begin to dig a hibernaculum, or den, in which to pass the winter.

Always keep in mind that hibernation is not the only reason why tortoises and turtles stop eating. Disease, parasites and improper housing conditions (particularly inadequate temperatures), among many other factors will cause a tortoise to eat less or to stop eating.

Only healthy specimens who have been eating well and who have not experienced recent or unresolved illness or stress should be allowed to hibernate. It is vital to know the animal’s history.

Malnourished animals or those kept at incorrect temperatures should not undergo hibernation. Records of the animal’s weight should indicate no loss. If weights are unavailable, or if the individual is new to the collection and his history is unclear, it may be wise to delay hibernation until the next year.

Getting Him Ready for Bed

Be sure that your pet is fit to hibernate. In most cases, this should involve an annual pre-hibernation trip to your reptile veterinarian, for a physical examination and a review of dietary history to help to assess fitness for hibernation.

Begin by withholding food, but not water, for 10 to 14 days. Smaller animals or species should fast for a shorter time than should larger species or individuals. During the fast, maintain the tortoise within his POTZ (70 to 80 F or 22 to 28 C). This will allow him to clear his digestive tract of all food. This is important; undigested material will slowly rot, releasing toxins as the animal hibernates. The toxins can depress the immune system and shut down the digestive system.

Tortoises should be soaked daily or every other day in tepid water for 20 to 30 minutes; in water deep enough to reach their chins when the head is at rest. Soaking will ensure that the tortoise has every opportunity to be well hydrated and will also encourage him to evacuate wastes from his bladder and colon.

After 10 to 14 days kept in normal conditions, that is, within the POTZ, the tortoise should spend up to one week at room temperature 60 to 70 F or 16 to 21 C, before moving to the hibernaculum.

The temperature inside the hibernaculum should stay at 40 to 50 F (5 to 10 C) and must not rise above 55 to 60 F (15 to 16 C). Higher temperatures can speed up the metabolism and deplete fat stores, while colder temperatures are dangerously close to freezing.

You will need to build a hibernaculum. The purpose of the hibernaculum is to insulate the animal against exterior temperature fluctuations. Ambient temperature must be controlled and monitored. A maximum-minimum thermometer is strongly recommended.

The hibernaculum should be placed in a dark or dimly lit, draft free, secure room, free from disturbance. Several weeks prior to placing the animal into hibernation, you should set up the hibernaculum in the precise conditions that the tortoise will experience. This allows time to monitor the maximum and minimum temperatures under different weather circumstances, and will allow the opportunity to make changes if necessary.

Dehydration is a serious concern during the hibernation of tortoises in captivity. If soil is used, it must be kept moist, but not wet. A bowl of water can be placed near the tortoise to help increase humidity. To re-hydrate, soak him in tepid water for 30 minutes to an hour.

Monitoring is the Key

Once your tortoise has gone to sleep, you must monitor his health and the condition of the hibernaculum regularly. Always check:

A tortoise is weighed in grams. A mature, healthy tortoise will lose about one to two percent of his weight for every month of hibernation. After one month in hibernation, a 1,000-gram tortoise should weigh no less that 980 grams. Excessive weight loss may be a sign of a problem. (If he loses five percent of his pre-hibernation weight, it is time to wake him up).

Every seven days, in the case of small or juvenile reptiles, or every two weeks in the case of large, mature specimens, remove the tortoise from the hibernaculum. Check the hibernaculum for excessive or inadequate moisture, mold, insects or evidence of rodents.

Ending Hibernation

It is time to wake your tortoise if his weight loss is approaching acceptable levels, if he shows signs of increased activity or if he has simply spent enough time in hibernation. If there is any question of a medical problem wake your pet immediately, and seek veterinary advice. For more information, see Waking From Hibernation.